The present invention relates to a fabrication planning system and particularly to a fabrication planning system for scheduling fabrication backup operations in separately located fabrication facilities.
FIG. 1 is a schematic view showing a conventional fabrication system 100 containing Fabs 11 and 13, capable of fabricating semiconductor wafers. Fabs 11 and 13 are not identical in tool composition, but have similar and/or partially overlapping tool sets. Fabs 11 and 13 contain tool groups 11a˜11n and 13a˜13n, respectively. Tool groups 11a and 13a comprise tools 111 and 131, respectively. Tools in tool groups 11a˜11n and 13a˜13n are controlled by Manufacturing Execution Systems (MESs) 110 and 130, respectively. Although both Fabs 11 and 13 belong to fabrication system 100, they are not only geographically separated but also operate independently. Because of the independent operation, workloads allocated to Fab 11 cannot be processed in Fab 13, and vice versa. Even though Fab 13 is available as a backup, workload in Fab 11 remains idle when tool bottleneck occurs. Thus, some tools in Fab 13 may remain idle despite Fab 11 having wafer lots queued at a corresponding tool. The independent operation of Fabs 11 and 13 actually hinders the fabrication system 100 from optimum utilization.
While cross-Fab backup within a fabrication system is clearly desired, it is not routinely practiced due to great difficulty in coordinating capacity of independent fabrication facilities. Cross-Fab backup is presently planned and executed manually in the conventional fabrication system, which is an inefficient and mistake-prone process. Conventionally, planning for backup operation starts only when a tool bottleneck occurs. At the beginning of the backup planning stage, the backup demand of the bottlenecked tool is calculated according to WIP (work-in-process) profile and capacity of the bottlenecked tool. After the backup demand is determined, it is then determined whether a backup operation will be executed. Considerable communication is required when querying other Fabs for capable of providing backup support to the bottlenecked tool. Moreover, because backup planning starts only when a tool bottleneck occurs, latent tool bottlenecks are concealed. As a result, the backup operation cannot be arranged in advance, and the throughput of the Fab will be seriously hindered by the bottleneck.
Hence, there is a need for a fabrication system that addresses inefficient backup planning arising from the existing technology.